1. Field of Invention
This invention is a method for inhibiting cell proliferation using a class of indanone compositions never before considered for that purpose. As inhibitors of cell proliferation, the compositions are useful in the treatment of cancer, cardiovascular disease, e.g. restenosis, host graft rejection, gout, and other proliferative disorders as well as being potential therapeutics for autoimmune diseases, such as rheumatoid arthritis, lupus, type I diabetes, multiple sclerosis and similar disorders and diseases.
2. Description of the Art
The multicatalytic proteinase or proteasome is a highly conserved cellular structure that is responsible for the ATP-dependent proteolysis of most cellular proteins. The 20S (700-kDa) proteasome contains at least five distinct proteolytic activities that have a new type of mechanism involving a threonine residue at the active site (Coux, O., Tanaka, K. and Goldberg, A. 1996 Ann. Rev. Biochem. 65:801-47).
The 20S proteasome has been crystallized from the archaebacteria Thermoplasma acidophilum (Lowe, J., Stock, D., Jap. B., Zwickl, P., Bauminster, W., and Huber, R. 1995 Science 268:533-539). The archaebacterial 20S proteasome contains fourteen copies of two distinct types of subunits, .alpha. and .beta., which form a cylindrical structure consisting of four stacked rings. The top and bottom rings contain seven .alpha. subunits each whilst the inner rings contain seven .beta. subunits. A pore extends through the middle of the structure that contains the proteolytic active sites and proteins destined for degradation pass through this channel. The eukaryotic 20S proteasome is more complex than that of the archaebacteria because the number of distinct subunits has increased during evolution, however, the subunits can still be classed according to the .alpha. and .beta. nomenclature of archaebacteria according to their homology. Thus the quaternary structure of the eukaryotic complex is similar to that of the archaebacteria being comprised of two .alpha. and two .beta. rings. However, unlike the archaebacterial proteasome that primarily exhibits chymotrypsin-like proteolytic activity (Dahlmann, B., Kopp, F., Kuehn, L., Niedel, B., Pfeifer, G. 1989 FEBS Lett. 251:125-131, Seemuller, E., Lupas, A., Zuhl, F., Zwickl, P and Baumeister, W. 1995 FEBS Lett. 359:173; and Lowe, J., Stock, D., Jap, B., Zwickl, P., Bauminster, W. and Huber, R. 1995 Science 268:533-539), the eukaryotic proteasome contains at least five identifiable protease activities. These are termed chymotrypsin-like, trypsin-like and peptidylglutamyl-peptide hydrolyzing. Two other activities have also been described, one exhibiting a preference for cleavage of peptide bonds on the carboxyl side of branched chain amino acids and the other toward bonds between small neutral amino acids. (Orlowski, M. 1990 Biochemistry 29: 10289-10297).
Although the 20S proteasome contains the proteolytic core, it cannot degrade proteins in vivo unless it is complexed with a 19S cap at either end of its structure, which itself contains multiple ATPase activities. This larger structure is known as the 26S proteasome and rapidly degrades proteins that have been targeted for degradation by the addition of multiple molecules of the 8.5-kDa polypeptide, ubiquitin.
The first step towards the ubiquitination of a protein proceeds by activation of a ubiquitin molecule at its carboxyl terminal glycine residue by addition of ATP that creates a high energy thioester intermediate. This step is catalyzed by the ubiquitin-activating enzyme, E1. Ubiquitin is then transferred to the active cysteine residue of a ubiquitin-conjugating enzyme, E2. E2 enzymes attach ubiquitin to the E-amino groups of lysine residues on the substrate protein that is destined to be degraded. This process, in some cases also requires a ubiquitin ligase, E3. Repeated conjugation of ubiquitin to lysine residues of formerly bound ubiquitin moieties leads to the formation of multi-ubiquitin chains and creates a scaffold of ubiquitin around the substrate protein. Multi-ubiquitinated substrate proteins are recognized by the 26S proteasome and are degraded and the multi-ubiquitin chains are released from the complex and ubiquitin is recycled.
What causes a protein to become ubiquitinated and thus degraded is still under investigation. Clearly this must be a highly regulated series of events since the critical timing of specific protein degradation is crucial for many cell cycle functions. Several signals have been proposed which largely center upon internal structural sequences within the substrate itself. One such proposal is the "N-end rule" in which the amino terminal residue of a protein determines it's half life. Other proteins such as the cyclins contain a short sequence of highly conserved amino acids termed the "destruction box" that are apparently necessary for degradation. Furthermore "PEST" sequences, which consist of regions rich in proline, aspartate, glutamate, serine and threonine also seem to act as degradation signals. It is thought that such internal sequences act as recognition elements between the protein substrate and its specific ubiquitination machinery.
Two types of inhibitors that inhibit the proteolytic activity of the proteasome, have been described. Certain peptide aldehydes have been reported to inhibit the chymotrypsin-like activity associated with the proteasome (Vinitsky, A., Michaud, C., Powers, J. and Orlowski, M. 1992 Biochemistry 31:9421-9428; Tsubuki, S., Hiroshi, K., Saito, Y., Miyashita, N., Inomata, M., and Kawashima, S., 1993 Biochem.Biophys.Res.Commun. 196:1195-1201; Rock, K, l., Gramm, C., Rothstein, L., Clark K., Stein, R., Dick, L., Hwang, D., and Goldberg, A. L. 1994 Cell 78:761-771). These are N-acetyl-L-leucinyl-L-leucinal-L-norleucinal (ALLN) and a closely related compound, N-acetyl-L-leucinyl-L-leucinyl-methional (LLM) with a K.sub.i 's of 0.14 .mu.M. The most potent inhibitor of this type is a structurally related compound, N-carbobenzoxyl-L-leucinyl-L-leucinyl-L-norvalinal (MG 115) which exhibits a K.sub.i of 0.021 .mu.M. Although these peptide aldehydes are most effective against the chymotrypsin-like proteolytic activity of the proteasomes, careful studies have shown that they are non-specific protease inhibitors. More recent reports have described series of potent dipeptide inhibitors that have IC.sub.50 values in the 10-100 nM range in vitro (Iqbal, M., Chatterjee, S., Kauer, J. C., Das, M., Messina, P., Freed, B., Biazzo, W., and Siman, R. 1995 J.Med.Chem. 38:2276-2277) and a series of similarly potent in vitro inhibitors from .alpha.-ketocarbonyl and boronic ester derived dipeptides (Iqbal, M., Chatterjee, S., Kauer, J. C., Mallamo, J. P., Messina, P. A., Reiboldt, A., and Siman, R. 1996 Bioorg. Med.Chem. Lett 6:287-290).
Another report describes a class of compounds that exhibit specificity in inhibiting proteasome activity (Fenteany, G., Standaert, R. F., Lane, W. S., Choi, S., Corey, E. J., and Schreiber, S. L. 1995 Science 268:726-731). Lactacystin is a Streptomyces metabolite that specifically inhibits the proteolytic activity of the proteasome complex. This molecule was originally discovered for its ability to induce neurite outgrowth in a neuroblastoma cell line (Omura et al., 1991 J.Antibiot. 44:113) later it was shown to inhibit the proliferation of several cell types (Fenteany et al 1994 Proc.Nat'l. Acad.Sci. USA 91: 3358). By using radiolabelled lactacystin, binding studies by (Fenteany et al., 1995 Science 268:726-731) have identified the binding site and the mechanism of action. These studies have shown that lactacystin binds irreversibly to a threonine residue located at the amino terminus of the .beta. subunit of the proteasomes. A series of analogues based upon the structure of lactacystin were also investigated (Fenteany et al., 1995 Science 268:726-731). These studies indicated that the .beta.-lactone structure was essential for its inhibitory activity.
It is now well established that the proteasome is a major extralysosomal proteolytic system which is involved in the degradative pathways resulting in numerous and diverse cellular functions such as cell division, antigen processing and the degradation of short lived regulatory proteins such as transcription factors, oncogene products and cyclins (reviewed in Ciechanover, A. 1994 Cell 79:13-21). The primary function of the proteasome is to catalyze the proteolysis of proteins into small peptides. However, it has also been demonstrated that the ubiquitin-proteasome pathway can catalyze the regulated proteolytic processing of a large inactive precursor into an active protein. The best documented case of this involves the activation of the transcription factor NF-.kappa.B (Palombella, V. J., Rando, O. J., Goldberg, A. L., and Maniatis, T. 1994 Cell 78:773-785). The active form of NF-.kappa.B is a heterodimer consisting of a p65 and a p50 subunit. The latter is present in the cytosol of the cell in an inactive precursor form, namely p105, the 105-kDa polypeptide precursor of p50. The proteolytic processing of p105 to generate p50 occurs via the ubiquitin-proteasome pathway. Additionally, processed p50 and p65 is maintained in the cytosol as an inactive complex with the inhibitory protein I.kappa.B. Inflammatory signals activate NF-.kappa.B by initiating the signalling pathway for the complete degradation of I.kappa.B, and also stimulate the processing of p105 into p50. Thus two proteolytic events, both governed by the ubiquitin-proteasome pathway, are required for signal induced activation of NF-.kappa.B. What causes the termination of proteolysis of p105 following generation of p50 is not known but it has been proposed that the conformation of p50 may render it resistant to further processing and cause it to dissociate from the 26S complex.
The fact that the proteasome plays a critical event in the activation of NF-.kappa.B could be exploited clinically by the use of inhibitors directed towards proteasome proteolysis. In certain diseases the normal function of active NF-.kappa.B can be detrimental to human health as observed in inflammatory responses following bacterial, fungal or viral infection. Thus inhibitors of NF-.kappa.B activation, due to their ability to prevent secretion of cytokines, may have potential utility in the treatment of ARDS (acute respiratory distress syndrome) and AIDS. Since activation of NF-.kappa.B is also essential for angiogenesis, proteasome inhibitors may have utility in the treatment of those diseases associated with abnormal neovascularization.
p53 was first described as an oncoprotein but has since been shown to be involved in many cellular processes (reviewed by Ko, L. J. and Proves, C. 1996 Genes Dev. 10, 1054-1072). p53 has been shown to induce apoptosis in several haematopoietic cell lines (Oren, M., 1994 Semin. Cancer Biol. 5, 221-227) through the action of many different stimuli including DNA damage, viral infection and the removal of growth factors. However, it is important to note that apoptosis can be induced in a p53-independent manner for example by the action of glucocorticoids. Induction of p53 leads to cell growth arrest in the G1 phase of the cell cycle as well as cell death by apoptosis. Both of these functions allow p53 to control DNA damage thereby reducing the propagation of DNA mutations when cells divide. p53 arrests cells at G1 by inducing the cyclin-dependent kinase inhibitor, p21, which in turn causes an accumulation of the hypophosphorylated form of the retinoblastoma gene product. It is thought that p53 acts as a check point in the cell following DNA damage, it first causes an arrest in cell division and apoptosis. p53 degradation is known to be via the ubiquitin-proteasome pathway and disrupting p53 degradation is a possible mode of inducing apoptosis. Another potential utility of proteasome inhibitors may be in the treatment of diseases that result from abnormal cell proliferation.
It is well documented that the ubiquitin-proteasome pathway is critical for the regulated destruction of cyclins that govern the exit from mitosis and allow cells to progress into the next phase of the cell cycle. Thus inhibiting degradation of cyclins by using proteasome inhibitors causes growth arrest. Therefore another potential utility of proteasome inhibitors is their use in the treatment of diseases that result from an accelerated cell division. These include cancer, cardiovascular diseases such as myocarditis, restenosis following angioplasty, renal diseases such as lupus, polycystic kidney disease, fungal infections, dermatological diseases such as psoriasis, abnormal wound healing, keloids, immunological diseases such as autoimmunity, asthma, and allergy, acute and delayed hypersensitivity, graft versus host disease, transplant rejection and neuroimmunological diseases such as multiple sclerosis and acute disseminated encephalomyelitis.